Compact organic vapor jet printing print head

ABSTRACT

A first device is provided. The first device includes a print head, and a first gas source hermetically sealed to the print head. The print head further includes a first layer further comprising a plurality of apertures, each aperture having a smallest dimension of 0.5 to 500 microns. A second layer is bonded to the first layer. The second layer includes a first via in fluid communication with the first gas source and at least one of the apertures. The second layer is made of an insulating material.

This application is a divisional of U.S. patent application Ser. No.12/729,479, filed Mar. 23, 2010, which in turn claims priority to, andthe benefit of, U.S. Provisional Application Ser. No. 61,211,002,entitled Compact OVJP Print Head, filed Mar. 25, 2009, all of which areincorporated by reference in their entireties.

This invention was made with government support under DE-FC26-04NT42273awarded by the Department of Energy. The government has certain rightsin the invention.

FIELD OF THE INVENTION

The present invention relates to the deposition of organic materialsthrough a print head.

BACKGROUND

Opto-electronic devices that make use of organic materials are becomingincreasingly desirable for a number of reasons. Many of the materialsused to make such devices are relatively inexpensive, so organicopto-electronic devices have the potential for cost advantages overinorganic devices. In addition, the inherent properties of organicmaterials, such as their flexibility, may make them well suited forparticular applications such as fabrication on a flexible substrate.Examples of organic opto-electronic devices include organic lightemitting devices (OLEDs), organic phototransistors, organic photovoltaiccells, and organic photodetectors.

More details on OLEDs can be found in U.S. Pat. No. 7,279,704, which isincorporated herein by reference in its entirety.

Various ways to deposit the organic materials used to fabricate organicdevices are known, such as vacuum thermal evaporation, solutionprocessing, organic vapor phase deposition, and organic vapor jetprinting.

SUMMARY OF THE INVENTION

Some aspects of the invention relate to a nozzle geometry useful fororganic vapor jet printing.

In one embodiment, a first device is provided. The device includes aprint head. The print head further includes a first nozzle hermeticallysealed to a first source of gas. The first nozzle has an aperture havinga smallest dimension of 0.5 to 500 microns in a direction perpendicularto a flow direction of the first nozzle. At a distance from the apertureinto the first nozzle that is 5 times the smallest dimension of theaperture of the first nozzle, the smallest dimension perpendicular tothe flow direction is at least twice the smallest dimension of theaperture of the first nozzle.

The print head may include a plurality of first nozzles hermeticallysealed to the first source of gas.

The print head may include a second nozzle hermetically sealed to asecond source of gas different from the first source of gas. The secondnozzle has an aperture having a smallest dimension of 0.5 to 500 micronsin a direction perpendicular to a flow direction of the second nozzle.At a distance from the aperture into the second nozzle that is 5 timesthe smallest dimension of the aperture of the second nozzle, thesmallest dimension perpendicular to the flow direction is at least twicethe smallest dimension of the aperture of the second nozzle.

The print head may include a third nozzle hermetically sealed to a thirdsource of gas different from the first and second sources of gas. Thethird nozzle has an aperture having a smallest dimension of 0.5 to 500microns in a direction perpendicular to a flow direction of the thirdnozzle. At a distance from the aperture into the third nozzle that is 5times the smallest dimension of the aperture of the third nozzle, thesmallest dimension perpendicular to the flow direction is at least twicethe smallest dimension of the aperture of the third nozzle.

The print head may comprise a plurality of first nozzles hermeticallysealed to the first source of gas, a plurality of second nozzleshermetically sealed to the second source of gas, and/or a plurality ofthird nozzles hermetically sealed to the third source of gas.

There are a number of different ways that a nozzle may meet thegeometrical considerations discussed above. The first nozzle may aconstant cross section from the aperture to a distance from the apertureinto the first nozzle that is 2 times the smallest dimension of theaperture of the first nozzle. The smallest dimension of the first nozzlein a direction perpendicular to a flow direction of the first nozzle maycontinuously increase with distance from the aperture of the firstnozzle for distances in the range of zero to 2 times the smallestdimension of the aperture of the first nozzle. The smallest dimension ofthe first nozzle in a direction perpendicular to a flow direction of thefirst nozzle may increases linearly with distance from the aperture ofthe first nozzle for distances in the range of zero to 2 times thesmallest dimension of the aperture of the first nozzle.

The nozzle may be formed from a variety of materials. Silicon isparticularly preferred. Metals and ceramics are also preferred

Preferred ranges for the smallest dimension of the aperture of the firstnozzle in a direction perpendicular to a flow direction of the firstnozzle include 100 to 500 microns, 20 to 100 microns, and 0.5 to 20microns.

Preferred shapes for the cross section of the first nozzle perpendicularto the flow direction of the first nozzle include circular andrectangular.

The first device may be used with multiple gas streams, which may carrydifferent organic materials. The first device preferably includes firstand second sources of gas, and a thermal barrier disposed between theprint head and the first and second sources of gas. Preferably,independently controllable heat sources are provided for each of theprint head, the first source of gas, and the second source of gas.

The first device may be used with gas streams that may carry multipleorganic materials in each gas stream, where different organic materialsmay be sublimated in different chambers having independent temperaturecontrol. Preferably, the first source of gas includes a firstsublimation chamber and a second sublimation chamber. The first gassource may be separated from the print head by a thermal barrierdisposed between the print head and the first source of gas.Independently controllable heat sources may be provided for each of theprint head, the first sublimation chamber and the second sublimationchamber.

The first device may be used to eject a jet of gas from the firstnozzle, as well as the other nozzles.

While the first device is being used to eject jets of gas from thenozzles, different and independently controllable temperatures may bemaintained at the print head and the first, second, and/or third sourcesof gas. In one embodiment, the gas provided by the first source of gasincludes a first organic material having a first sublimationtemperature, and the gas provided by the second source of gas includes asecond organic material having a second sublimation temperature at least10 degrees Celsius different from the sublimation temperature of thefirst organic material.

Some aspects of the invention relate to a microfluidic print head usefulfor organic vapor jet printing.

In one embodiment, a first device is provided. The first device includesa print head, and a first gas source hermetically sealed to the printhead. The print head further includes a first layer further comprising aplurality of apertures, each aperture having a smallest dimension of 0.5to 500 microns. A second layer is bonded to the first layer. The secondlayer includes a first via in fluid communication with the first gassource and at least one of the apertures. The second layer is made of aninsulating material.

The first layer of the first device may include a channel that providesfluid communication within the first layer between the first via of thesecond layer and apertures of the first layer. The second layer of thefirst device may also, or instead, include a channel that provides fluidcommunication within the second layer between the first via of thesecond layer and apertures of the first layer. The first layer and/orsecond layers may further include a heat source.

The first device may include a third layer disposed between the firstand second layers and bonded to the first layer and the second layer.The third layer may include a channel that provides fluid communicationbetween the first via of the second layer and apertures of the firstlayer. The third layer may further include a heat source.

A plurality of apertures may be in fluid communication with the firstgas source.

The first device may further include a second gas source hermeticallysealed to the print head. The first via of the second layer may be influid communication with a first group of apertures of the first layer.The second layer may further include a second via in fluid communicationwith the second gas source and a second group of apertures of the firstlayer. The first device may further include a third gas sourcehermetically sealed to the print head. The second layer may furtherinclude a third via in fluid communication with the third gas source anda third group of apertures of the first layer.

A gas source, such as the first gas source or any other gas source mayinclude multiple organic sources. Multiple vias connected to differentgas sources may be in fluid communication with the same aperture,resulting in a mix of gases at the aperture. For example, the first viamay be in fluid communication with a first organic source, while asecond via is in fluid communication with a second organic source. Thefirst and second vias may both in fluid communication with a first groupof apertures of the first layer. The print head, the first organicsource and the second organic source each have independentlycontrollable heat sources.

The first device may further include a first valve for controlling gasflow to the first organic source and a second valve for controlling gasflow to the second organic source. The first and second valves may bethermally insulated from the heat sources.

The first layer is preferably formed from silicon.

The first layer is preferably bonded to the second layer using a bondselected from the group consisting of a fusion bond, cold weld, ananodic bond, and a eutectic bond. If additional layers are present inthe print head, such as a third layer or other layers, they arepreferably bonded using these types of bonds. In one embodiment, it ispreferred that the first and second layers are bonded to each otherusing an anodic bond. In another embodiment, it is preferred that athird layer is placed between the first and second layers, the first andthird layers are bonded with a eutectic bond or fusion bond, and thethird and second layers are bonded, preferably with an anodic bond.

The print head may further include a microelectromechanical switchadapted to block or allow fluid communication between the first via andthe at least one of the apertures depending upon the state of theswitch.

At least one aperture may be formed in a protrusion from the print head.

The thickness of the print head is preferably between 50 and 500microns.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows cross sections of four different nozzle geometries.

FIG. 2 shows cross sections of four different nozzle geometries taken ina direction perpendicular to gas flow.

FIG. 3 shows a perspective drawing of an OVJP print head and mounting.

FIG. 4 shows an exploded view of print head.

FIG. 5 shows photographs of parts of a print head.

FIG. 6 shows a proof of a mask including channels and vias.

FIG. 7 shows a cross-section of a rectangular nozzle that was actuallyfabricated, as well as a scanning electron microscope photograph of thenozzle inlets etched into Si.

FIG. 8 shows a photograph of nozzle side of completed print head, aswell as a scanning electron micrograph (SEM) of a portion of the nozzlearray 802 and a SEM of a nozzle aperture.

FIG. 9 shows a modeled deposition profile.

FIG. 10 shows modeled pressure and temperature profiles.

FIG. 11 shows a model used in a circuit analysis of a nozzle array.Fluidic resistances were estimated and even distribution of vapor to allnozzles in the array was verified.

FIG. 12 shows a modeled heat transfer profile in the vicinity of a 20 mmwide nozzle.

FIG. 13 shows a plot of the height of the center of a wafer relative toouter rim as function of temperature, as well as a schematic of thesetup used to obtain the data.

FIG. 14 shows a plot of displacement vs. voltage for calibration of aPhilTech RZ-25 displacement sensor on an ITO target.

FIG. 15 shows a process flow for preparing silicon and borosilicatewafers for microfabrication.

FIG. 16 shows steps of Si and borosilicate processing used to fabricatea print head.

FIG. 17 shows an exploded drawing of an OVJP feedthrough.

FIG. 18 shows a configuration of an OVJP system with alignment opticsand height sensor installed.

FIG. 19 shows optical micrographs of 35 nm thick lines of AlQ, Aluminumtris(quinoline-8-olate), drawn using the OVJP print head

FIG. 20 shows SEM images of 35 nm thick lines of AlQ drawn using an OVJPprint head

FIG. 21 shows atomic force micrograph images of 35 nm thick AlQ linesdrawn using an OVJP print head.

FIG. 22 shows optical micrograph and profilometer images of a thick lineof material drawn using an OVJP print head.

FIG. 23 shows linescan data from AlQ lines drawn using an OVJP printhead.

FIG. 24 shows a confocal epifluorescence micrograph of lines drawn usingan OVJP print head.

DETAILED DESCRIPTION

The pixels of a high definition display may consist of patterned red,green, and blue stripes that are about 30 μm wide. The edges ofdifferent color stripes may be separated by only 10 μm. For organicpixels, it is preferred that the pattern have a sharpness of about 5 μmto avoid unintended overlap of materials due to overspray. Thesedimensions may be useful for other organic devices as well such asorganic transistors or other devices.

One way to deposit organic materials for use in a high definitiondisplay, or other device that uses organic materials, is organic vaporjet deposition (OVJP). In order to become a viable display manufacturingtechnology, it is preferred that organic vapor jet printing be capableof patterning organic films with 5 μm sharpness. It is also preferredthat the OVJP process be able to deposit multiple lines simultaneously.Multiple nozzles are one way to achieve the deposition of multiple linessimultaneously.

Modeling of the organic vapor jet printing process for 30 μm scalefeatures using Direct Simulation Monte Carlo (DSMC) techniques hasrevealed that a nozzle aperture to substrate separation of <5 μm isrequired to achieve the desired feature sharpness, assuming a nozzleaperture width of 20 μm. This estimate is supported by a rule of thumbobserved in previous OVJP studies, that printing resolution scales withnozzle to substrate separation.

However, prior techniques may not be well adapted to producing an arrayof 20 μm nozzles designed to operate within 5 μm of the substrate.First, a nozzle plate having height tolerances consistent with anoptically flat substrate is desirable for operating at these dimensionsacross a reasonable number of simultaneously deposited lines, to providethe best possible height tolerances. Prior techniques may not have beenwell adapted to provide such a nozzle plate. For an array of multiplenozzles, flatness is preferably maintained over a relatively large area.Secondly, it is preferred during OVJP to keep the nozzle plate hot, somaterials that maintain their strength up to 300° C. are desirable.Additionally, thermal expansion may interfere with maintaining thesetight tolerances, so materials that resist thermal expansion or do notresult in deformation as a result of thermal expansion are desirable.Finally, the gas dynamics of the nozzle-substrate system indicate that athree dimensional structure is preferred.

Silicon micromachining, or more generally semiconductor micromachining,provides a way to meet these demanding specifications. Fabrication stepscan be performed on highly polished wafers, eliminating heightvariation. The Si/SiO₂ system is stable across the applicable range oftemperatures for organic vapor deposition. Silicon also has a much lowercoefficient of thermal expansion than most metals. Tapered nozzles canbe fabricated using anisotropic etchants and multilayer structures canbe fabricated using silicon on insulator wafers and wafer bondingtechniques. Such techniques have been well developed in the field ofmicrofluidics. Microfluidics is the application of microfabricationtechniques to liquid and vapor transport systems and has been used inthe field of inkjet printing. Similar techniques may also be applied tometals and ceramics.

Interfacing a microfabricated device with the outside world presentsadditional issues. In the case of OVJP, the desire to operate attemperatures over 300° C. poses presents even more issues not present inmany other fields. An OVJP system may have a user serviceable vaporgeneration system, which means that an organic material is stored in astructure that is both durable and macroscopic. This, in turn, meansthat the organic vapor may be transported to the print head usingrelatively large bore metal tubes. As described herein, using wellchosen intermediate materials; it has been demonstrated that a bakeablegas tight seal may be provided between a metal manifold and a siliconnozzle plate.

Some aspects of the invention relate to a nozzle geometry useful fororganic vapor jet printing.

In one embodiment, a first device is provided. The device includes aprint head. The print head further includes a first nozzle hermeticallysealed to a first source of gas. The first nozzle has an aperture havinga smallest dimension of 0.5 to 500 microns in a direction perpendicularto a flow direction of the first nozzle. At a distance from the apertureinto the first nozzle that is 5 times the smallest dimension of theaperture of the first nozzle, the smallest dimension perpendicular tothe flow direction is at least twice the smallest dimension of theaperture of the first nozzle.

FIG. 1 illustrates the dimensions referred to in the previous paragraph,as well as some geometries that meet the criteria. Figures throughoutthis application are not necessarily drawn to scale. FIG. 1 shows crosssections of four different nozzle geometries, where the cross section istaken in a direction parallel to gas flow in the nozzle, and also in adirection that shows a smallest dimension at the nozzle aperture. Ineach geometry, an aperture has a smallest dimension 101 in a directionperpendicular to the flow direction of the nozzle. The “aperture” isdefined by the point at which this smallest dimension reaches a minimum,i.e, where gas flow through the nozzle is most constricted. Each nozzlealso has a distance 102 from the aperture into the nozzle that is 5times the smallest dimension of the aperture. Each nozzle also has adimension 103 that is the smallest dimension perpendicular to the flowdirection at distance 102 from the aperture into the first nozzle. Asillustrated, dimension 103 is at least twice the dimension 101. Nozzle110 has sloped sides that reach a point at the aperture. Nozzle 120 hassloped sides for a large part of the nozzle, but the sides are verticalfor a small distance at the aperture. In this case, where there is afinite distance in the flow direction of the nozzle over which thesmallest dimension reaches a minimum, the “aperture” is the pointclosest to the substrate at which the smallest is at a minimum. Nozzle120 may have better mechanical strength may be easier to fabricate witha consistent aperture size than nozzle 110. Nozzle 130 has sloped sidesthat reach a point, but widen out slightly before reaching the bottom ofnozzle 130. Nozzle 130 illustrated that the aperture is not necessarilyat the point of the nozzle closest to the substrate. Nozzle 140 hasvertical sides, with a dramatic narrowing just as the gas flow exits thenozzle. Other nozzle geometries may also meet the criteria of theprevious paragraph.

FIG. 2 shows cross sections of four different nozzle geometries taken atthe aperture in a direction perpendicular to the gas flow. The nozzlesfor which cross sections are taken in FIG. 2 do not necessarilycorrespond to those of FIG. 1. The arrow in each aperture represents the“smallest dimension” of the aperture. In mathematical terms, at thesmallest dimension, the arrow length is either at a local maximum (forthe circle, oval and triangle) or is constant (for the rectangle) withrespect to translation of the whole arrow in a direction perpendicularto the arrow, and the “smallest” dimension is the smallest local maximumor constant for which this occurs. FIG. 2 shows cross sections ofapertures 210, 220, 230 and 240 having circular, oval, rectangular andtriangular cross sections, respectively. A rectangular aperture is themost preferred shape for depositing lines, and is also a relatively easyshape to obtain in a nozzle etched in silicon. However, other shapes maybe used.

The print head may include a plurality of first nozzles hermeticallysealed to the first source of gas.

The print head may include a second nozzle hermetically sealed to asecond source of gas different from the first source of gas. The secondnozzle has an aperture having a smallest dimension of 0.5 to 500 micronsin a direction perpendicular to a flow direction of the second nozzle.At a distance from the aperture into the second nozzle that is 5 timesthe smallest dimension of the aperture of the second nozzle, thesmallest dimension perpendicular to the flow direction is at least twicethe smallest dimension of the aperture of the second nozzle.

The print head may include a third nozzle hermetically sealed to a thirdsource of gas different from the first and second sources of gas. ° Ilethird nozzle has an aperture having a smallest dimension of 0.5 to 500microns in a direction perpendicular to a flow direction of the thirdnozzle. At a distance from the aperture into the third nozzle that is 5times the smallest dimension of the aperture of the third nozzle, thesmallest dimension perpendicular to the flow direction is at least twicethe smallest dimension of the aperture of the third nozzle.

The print head may comprise a plurality of first nozzles hermeticallyscaled to the first source of gas, a plurality of second nozzleshermetically sealed to the second source of gas, and/or a plurality ofthird nozzles hermetically sealed to the third source of gas.

There are a number of different ways that a nozzle may meet thegeometrical considerations discussed above. The first nozzle may have aconstant cross section from the aperture to a distance from the apertureinto the first nozzle that is 2 times the smallest dimension of theaperture of the first nozzle. The smallest dimension of the first nozzlein a direction perpendicular to a flow direction of the first nozzle maycontinuously increase with distance from the aperture of the firstnozzle for distances in the range of zero to 2 times the smallestdimension of the aperture of the first nozzle. The smallest dimension ofthe first nozzle in a direction perpendicular to a flow direction of thefirst nozzle may increase linearly with distance from the aperture ofthe first nozzle for distances in the range of zero to 2 times thesmallest dimension of the aperture of the first nozzle.

The nozzle may be formed from a variety of materials. Silicon ispreferred.

Preferred ranges for the smallest dimension of the aperture of the firstnozzle in a direction perpendicular to a flow direction of the firstnozzle include 100 to 500 microns, 20 to 100 microns, and 0.5 to 20microns.

Preferred shapes for the cross section of the first nozzle perpendicularto the flow direction of the first nozzle include circular andrectangular.

The first device may be used with multiple gas streams, which may carrydifferent organic materials. The first device preferably includes firstand second sources of gas, and a thermal barrier disposed between theprint head and the first and second sources of gas. Preferably,independently controllable heat sources are provided for each of theprint head, the first source of gas, and the second source of gas.

The first device may be used with gas streams that may carry multipleorganic materials in each gas stream, where different organic materialsmay be sublimated in different chambers having independent temperaturecontrol. Preferably, the first source of gas includes a firstsublimation chamber and a second sublimation chamber. The first gassource may be separated from the print head by a thermal barrierdisposed between the print head and the first source of gas.Independently controllable heat sources may be provided for each of theprint head, the first sublimation chamber and the second sublimationchamber. A variety of heat sources may be used. For example, resistiveplates on the surface of the print head may be used, or heat sources maybe incorporated into the layers of a print head, for example asresistive elements embedded in one or more layers of the print head.

The first device may be used to eject a jet of gas from the firstnozzle, as well as the other nozzles.

While the first device is being used to eject jets of gas from thenozzles, different and independently controllable temperatures may bemaintained at the print head and the first, second, and/or third sourcesof gas. In one embodiment, the gas provided by the first source of gasincludes a first organic material having a first sublimationtemperature, and the gas provided by the second source of gas includes asecond organic material having a second sublimation temperature at least10 degrees Celsius different from the sublimation temperature of thefirst organic material. The difference in the sublimation temperature isa feature that embodiments of the invention can accommodate much morereadily that other designs, but is not needed to take advantage of otheraspects of embodiments of the invention. For example, separate sourcesallow the mix of materials to be continuously varied, whethersublimation temperatures are similar or different.

Some aspects of the invention relate to a microfluidic print head usefulfor organic vapor jet printing.

The first device may further include a first valve for controlling gasflow to the first organic source and a second valve for controlling gasflow to the second organic source. The first and second valves may bethermally insulated from the heat sources.

The first layer is preferably formed from silicon.

The first layer is preferably bonded to the second layer using a bondselected from the group consisting of a fusion bond, cold weld, ananodic bond, and a eutectic bond. If additional layers are present inthe print head, such as a third layer or other layers, they arepreferably bonded using these types of bonds. In one embodiment, it ispreferred that the first and second layers are bonded to each otherusing an anodic bond. In another embodiment, it is preferred that athird layer is placed between the first and second layers, the first andthird layers are bonded with a eutectic bond or fusion bond, and thethird and second layers are bonded, preferably with an anodic bond.

The print head may further include a microelectromechanical switchadapted to block or allow fluid communication between the first via andthe at least one of the apertures depending upon the state of theswitch.

At least one aperture may be formed in a protrusion from the print head.

The thickness of the print head is preferably between 50 and 500microns. The thickness of the printhead includes all layers from a firstlayer that includes the nozzles through and including a second layerthat includes vias.

In one embodiment, an organic vapor jet deposition system 300 isprovided. FIG. 3 shows a perspective drawing of OVJP system 300,including print head 310 and mounting. System 300 was actually made andoperated. System 300 includes a print head 310 containing flow channelsand nozzle arrays, which are illustrated in more detail in FIGS. 4though 6. Six organic vapor sources 320 (also referred to as “gassources”) are welded to a manifold 330 which is then hermetically sealedto the print head. One structure for a vapor source is illustrated inmore detail in FIG. 17. Manifold 330 is preferably fabricated from amaterial that maintains its shape at the print head operatingtemperatures, such as Kovar controlled expansion steel. Print head 310may clamped to manifold 330 and sealed using a high temperatureperfluroelastomer gasket, to achieve a hermetic seal between the organicvapor sources 320 and print head 310. Other methods of achieving ahermetic seal may also be used, such as anodic bonding of the print headto a Kovar backplate. Organic material is housed within heated tubesthat are laser welded to the Kovar manifold, which can be better seen inFIG. 17. Organic vapor sources 320 consist of heated tubes enclosingorganic source cells. This assembly is affixed to a 8″ in Conflat flange(manifold 330) which serves as both a structural member and a gasfeedthrough. The vapor generators are connected to ports on manifold 330through welded stainless steel bellows 340. Bellows 340 act as expansionjoints. Since organic vapor sources 320 may expand when heated, aflexible coupling is desirable between manifold 330 and vapor generators320 to avoid thermal stress than might be transmitted to and deformprint head 310.

Vapor generators 320, bellows 340, manifold 330, and associated fittingsform a clear 0.3 in inner diameter conduit stretching from the top ofthe manifold 330 to print head 310. Organic material is placed in avented capsule at the end of a glass rod and inserted into the conduit.When a rod is inserted, the organic material it contains is situatedinside the heated vapor generator. The top of the conduit is then sealedto the outer diameter of the glass rod using a Swagelok Ultratorrfitting. A thermocouple threaded through inner diameter of the glass rodprovides temperature readings inside the vapor generator. Carrier gas isfed into the conduit through a bored through tee adaptors between thefeedthrough and the Ultratorr fitting. These features may be seen moreclearly in FIG. 17.

FIG. 4 shows an exploded view of print head. A first layer 410 of theprint head includes a plurality of apertures, which preferably have thedimensions described with respect to FIGS. 1 and 2. First layer 410 ispreferably made from silicon, which can be readily patterned to includedesired nozzle geometries with known technologies developed, forexample, in the context of semiconductor processing. First layer 410includes a plurality of nozzles 415 patterned therein having apertures.First layer 410 is bonded to second layer 420. Preferred bonding methodsinclude fusion bonding, anodic bonding, cold welding and eutecticbonding. Second layer 420 is preferably made of an insulating material,to limit heat conduction from gas sources and to enable the temperatureof first layer 410 to be controlled independently of the temperature ofgas sources. Second layer 420 is bonded to first layer 410. Second layer420 includes vias 422 that are in fluid communication with nozzles 415.As illustrated, channels 424 etched into second layer 420 provide fluidcommunication between vias 422 and nozzles 415. Ohmic contacts 440 areevaporated over the front of first layer 410 to allow the nozzle plateto be addressed by a heating current.

In a print head actually fabricated and used as a part of a depositionsystem, first layer 410 was a silicon wafer, second layer 420 was aborosilicate wafer, and the two layers were bonded through anodicbonding. FIG. 5 shows photographs of a first layer 510 and a secondlayer 520 that were actually fabricated.

First layer 410 may include channels that provides fluid communicationwithin the first layer between vias 422 and nozzles 415, instead of orin addition to channels in second layer 420. First layer 410 may furtherinclude a heat source, such as heating contacts 440.

A third layer (not shown) may be disposed between the first layer 410and second layer 420, and bonded to first layer 410 and second layer420. Preferred bonding methods are as described in the previousparagraph. In this situation, first layer 410 would be considered to be“bonded to” second layer 420. The third layer may include a channel thatprovides fluid communication between vias 422 and nozzles 415, insteadof or in addition to channels in layers 410 and/or 420. The third layermay further include a heat source.

As illustrated in FIG. 4, a plurality of nozzles 415 may be in fluidcommunication with a single gas source, such as a first gas source. Oneway to achieve this is to have a channel connect a via to a plurality ofnozzles.

FIG. 6 shows a proof of a mask 600 including channels 610 and vias 620.The structure of FIG. 6 could be applied, for example, to a borosilicatewafer and used as second layer 420 of FIG. 4. Acute angles are avoidedto reduce stress. Channels 610 are oriented radially and given gentlecurvature to further reduce stress concentrations. Channels 610 formthree fluidic circuits. Circuit 612 allow two different dopants in acommon host to be fed into separate nozzle array. Circuit 614 allowshost and dopant materials to mix before being ejected from a nozzlearray. Circuit 616 feeds material from a single source to a nozzlearray.

As can be seen from FIG. 4, multiple gas sources may be hermeticallysealed to a print head. As can be seen from FIG. 6, channels can be usedto route gas from multiple sources in a wide variety of ways. Forexample, first and second, or first second and third gas sources,hermetically sealed to a print head, may each be in fluid communicationwith their own separate nozzle arrays. This would occur, for example, ifthe structure of FIG. 6 were adjusted to include three circuits similarto circuit 616. In this situation, the first device may further includea second gas source hermetically scaled to the print head. The first viaof the second layer may be in fluid communication with a first group ofapertures of the first layer. The second layer may further include asecond via in fluid communication with the second gas source and asecond group of apertures of the first layer. The first device mayfurther include a third gas source hermetically sealed to the printhead. The second layer may further include a third via in fluidcommunication with the third gas source and a third group of aperturesof the first layer.

Multiple vias connected to different gas sources may be in fluidcommunication with the same aperture, resulting in a mix of gases at theaperture. One, two, three, or more gases from different sources may bemixed in this way, as illustrated by circuits 612, 614 and 616. Forexample, the first via may be in fluid communication with a firstorganic source, while a second via is in fluid communication with asecond organic source. The first and second vias may both in fluidcommunication with a first group of apertures of the first layer. Theprint head, the first organic source and the second organic source eachhave independently controllable heat sources.

In addition to mixing gases from different sources in circuits in theprint head, a gas source, such as the first gas source or any other gassource, may include multiple organic materials either from the sameevaporation chamber or different evaporation chambers. However, mixingin the print head allows for maximum flexibility in terms of separatelycontrolling parameters such as temperature and gas flow in each chamberwhere organic material is sublimated. This may be highly desirable, forexample, where two organic materials have significantly differentsublimation temperatures. Rates of sublimation can be more readilycontrolled. In addition, where sublimation temperatures are dramaticallydifferent, a temperature desirable to sublimate one material may bedetrimental to a different material.

FIG. 7 shows a cross-section 700 of a rectangular nozzle 740 that wasactually fabricated. Nozzle 740 was fabricated in a first layer 710 thatwas made of silicon. The silicon wafer used to create first layer 710started out thicker than 50 microns to allow for protrusions, but had afinal thickness of 50 microns. Nozzle 740 has an aperture 730 that islocated in a protrusion 720 from first layer 710. Aperture 730 has asmallest dimension of 20 microns. Protrusion 720 protrudes 50 micronsfrom first layer 710. It is intended that nozzle 740 be used in closeproximity to a substrate, such that the nozzle—substrate separationdistance is about 5 microns. Protrusion 720 allows for gas expelled fromthe nozzle to escape without needing to travel through a 5 micron thickspace all the way to the edge of first layer 710. The angle between thenozzle wall and the plane of first layer 710 is 54.74 degrees, which isreadily achieved using known silicon etching technology involvingselective etching of the <100> plane of Si by KOH. FIG. 7 also showsimage 750, showing nozzle inlets etched into Si viewed under a scanningelectron microscope.

FIG. 8 shows a photograph 800 of nozzle side of completed print head.Nozzle array 802 is the array of high aspect-ratio rectangles in thecenter of the photograph. Bumpers 804 appear as dark squares. Largerbumpers are located farther away from nozzle array, while smallerbumpers are located near and interspersed with nozzle array 802. Bumpers804 are helpful in maintaining a desired substrate—nozzle separationduring deposition. Bumpers 804 are useful in a laboratory context, butmay or may not be present in a commercial embodiment. A displacementsensor window 806 is also shown. Displacement sensor window 806 providesa way to see the substrate when the nozzle is in use, and, for example,to measure substrate nozzle separation, or to position the nozzles basedon alignment marks or other features on a substrate. FIG. 8 also shows ascanning electron micrograph (SEM) 820 of a portion of nozzle array 802.FIG. 8 also shows a SEM of a nozzle aperture of nozzle array 802.

The structure illustrated and photographed in FIGS. 5 through 8 wasactually fabricated. The print head is composed of two bonded wafers(first and second layers). The bottom most wafer is the nozzle plate,which was 100 μm thick silicon, which is shown in FIGS. 7 and 8. A totalof 128 nozzles are etched into the plate. The nozzles have a bottomaperture of dimensions 20 μm by 200 μm with the long axis correspondingto the direction of substrate travel so as to produce narrow lines. Thesmallest dimension of these apertures is 20 μm. The nozzles are arrangedin four banks of 32 each and some of the banks are offset relative toeach other to allow printing of multiple side by side stripes. Each ofthe banks can deposit different organic vapor formulationssimultaneously. Anisotropic etching produces a nozzle inlet much widerthan the outlet. The underside of the print head, the side facing thesubstrate, is etched back so that the nozzle tips and other features areelevated beyond the wafer surface. Elevated nozzle tips allow thenozzles to be brought close to the substrate while still allowingcarrier gas to easily escape in the gap between the print head andsubstrate. A network of raised bumpers around the nozzles protects thenozzle tips from against crashing into the substrate. The nozzle plateis ported with optical windows to allow for the incorporation of anoptical displacement sensor to measure position relative to thesubstrate.

The channel and insulator layer (the second layer), which is shown inFIGS. 5 and 6, is made of 500 μm thick borosilicate glass. The nozzlesare fed by 100-200 μm deep fluidic channels etched into the side of theglass wafer facing the nozzle plate. These channels are fed through viaswhich extend through the thickness of the wafer. When the channel layerand insulator layer are bonded, a set of three fluidic independentfluidic circuits is formed. Vapor can be fed through any of the six viasand will emerge from the nozzles as dictated by the circuit layout.

The print head illustrated in FIGS. 5 through 8 was incorporated into aorganic vapor jet printing system 300 as illustrated in FIG. 3. Asdescribed with respect to FIG. 3, the print head rests on a Kovarmanifold. It is sealed to the manifold with a custom cut rubber gasketand held in place with stainless steel and Inconel clamps. Hightemperature rubbers such as Kalrez can be used for the gasket. Otherpackaging strategies, such as anodic bonding the print head to a Kovarbackplane, may be used. It is believed that a metal backplane willprovide a more robust sealing surface for the print head.

Effects of the nozzle and print head to substrate gap can be modeledmathematically. The flow of carrier gas through the print head tosubstrate gap can be modeled using the lubrication approximation forincompressible viscous flows. All non-radial components of flow areignored. The characteristic length defining flow is the print head tosubstrate gap, h. Pressure variation over this length is negligible, andgas expansion over the radial dimension can be approximated using theideal gas law. The average velocity of vapor flow is given by eq II.A.1.μ is viscosity, P is pressure, T is temperature, R is the ideal gasconstant, r is radius, and J is molar flow rate.

$\begin{matrix}{\left\langle v \right\rangle = {{\frac{- h^{2}}{12\mu}\frac{\mathbb{d}P}{\mathbb{d}r}} = {\frac{J}{2\pi\;{hr}}\frac{RT}{P}}}} & {{{Eq}.\mspace{14mu}{II}.A}{.1}}\end{matrix}$This can be expressed as differential equation Eq.II.A.2 and solved. iand o subscripts denote input and output conditions.

$\begin{matrix}{{\frac{\mathbb{d}P^{2}}{\mathbb{d}r} = {- \frac{12J\;\mu\;{RT}}{\pi\;{rh}^{3}}}}{{P_{i}^{2} - P_{o}^{2}} = {\frac{12J\;\mu\;{RT}}{\pi\; h^{3}}{\ln\left( \frac{r_{o}}{r_{i}} \right)}}}} & {{{Eq}.\mspace{14mu}{II}.A}{.2}}\end{matrix}$Assuming an outer radius of 50 mm, and inner radius of 10 mm, carriergas viscosity of 2.5×10⁻⁵ kg/m*s, a molar flow rate equivalent to 2sccm, and negligible pressure at the outer edge of print head, thepressure on the inside of the disc is roughly 3500 Pa.

Intuitively, the largest pressure drop will occur between in the gapbetween the lower tip of the nozzle and the substrate. Assuming thedownstream end of this gap is at 3,500 Pa, gas molecules inside willhave a mean free path of 3.5 μm. Particle to wall collisions will likelydominate in this regime, so it can be treated as a Knudsen flow. Usingthe transition probability method of Clausing, P J. Vac Sci. Tech 8636-46, the rate of molecular flow between two regions is given by eq.II.A.3, where J is rate of molecular flow, T and P are temperature andpressure, m is the molecular mass of the carrier gas, A is the area ofthe tube, and w is a transmission probability. Stanteler D. J. and D.Boeckman J. Vac Sci Tech. A 9 (4) 8 July/August 1991 calculated w=0.533for a wide rectangular conduit with a length to height ratio of 4:1.

$\begin{matrix}{{J = {{\frac{Aw}{4}\sqrt{\frac{8}{\pi\;{mk}_{B}T}}\left( {P_{1} - P_{2}} \right)} = {0.0023\frac{sccm}{Pa}\Delta\; P}}}{{for}\mspace{14mu}{gaps}\mspace{14mu}{in}\mspace{14mu}{parallel}}} & {{{Eq}.\mspace{14mu}{II}.A}{.3}}\end{matrix}$

A survey of possible nozzle designs by Direct Simulation Monte Carlotechniques suggests that a nozzle design with an inner and outer taperproduces the optimal flow pattern for high resolution deposition. Thefluidic resistance is in good agreement with the above analytical model,predicting a conductance of 0.0021 sccm/Pa. A rectangular nozzle tip ofcross section 20 μm by 200 μm m is recommended. The recommended nozzleto substrate separation is 3 to 5 μm. 32 such nozzles or more can besituated in an array. A large array of nozzles is beneficial, since itreduces the pressure differential between the vapor generators andsubstrate. The resulting deposition profile is expected to have a fullwidth at half maximum of 18 μm. Deposition is expected to drop off to10% of its centerline value in 40 μm, making it capable of accuratelydepositing within a 30 μm pixel bordered by 30 μm without significantlyintruding on neighboring pixels. The expected deposition profile isshown in FIG. 9 as a solid line, for a double tapered nozzle with 20 μmwide aperture and 5 μm tip to substrate gap. Height is in arbitraryunits. An ideal pixel filling deposition profile with height equal toprofile average over pixel width is shown in dashes.

FIG. 10 shows a modeled pressure profile 1010 and a modeled temperatureprofile 1020 for a double tapered nozzle with 20 μm wide aperture and 5μm tip to substrate gap. The barrier created by the nozzle body is thedark region in cross section. The profiles are symmetric, so showingonly half of the nozzle captures the relevant information.

Satisfactory deposition profiles can be achieved without an outer taperon the nozzle to match the inner taper of the nozzle, however this isless preferred because the conductivity of the simulated nozzlestructure drops by a factor of five. The effect becomes more pronouncedonce the reduced exit path of gas from the nozzle to the print head edgeis considered. The pressure required to yield a desired flow ratedilutes the organic in the vapor stream and enhances heat transferbetween the print head and substrate. This leads to a non-idealoperating regime. However, print heads without the underside taper haveproven to be effective deposition tools, and may be used because theyare easier to fabricate than a print head having a tapered underside.

Operating pressure increases, although not as severely, if the innertaper is deleted. Interestingly, however, the deposition profile takeson a double peaked structure, shown in FIG. 9. It is possible that theinner taper can be optomized to produce an optomized, mesa-likedeposition profile. Plasma etching can be used to fabricate a wide rangeof geometries.

Flow through vapor generators and channel array also be mathematicallymodeled. Volume flow rate for a rectangular conduit with short crosssectional dimension h and larger cross section dimension w is calculatedusing, eq II.B.I dervied from the incompressible Navier-Stokesequations. It is then converted to a molar flow rate using the ideal gaslaw. μ is viscosity and x is the axial dimension of the channel andpositive in the downstream direction. P, T are pressure and temperaturein the channel. R is the ideal gas constant.

$\begin{matrix}{{Q_{vol} = {{- \frac{\mathbb{d}P}{\mathbb{d}x}}\frac{h^{3}w}{12\mu}}}{Q_{= {mol}} = {{{- \frac{P}{RT}}\frac{\mathbb{d}P}{\mathbb{d}x}\frac{h^{3}w}{12\mu}} = {{- \frac{\mathbb{d}P^{2}}{\mathbb{d}x}}\frac{h^{3}w}{24\mu}}}}} & {{{eq}.\mspace{14mu}{II}.B}{.1}}\end{matrix}$The nozzle array can be analyzed by breaking it up into segments andapplying reasoning similar to Kirchoffs current law. A laminarcompressible flow through a nozzle generally scales as Q_(mol)˜P².However, due to the very small length scale, through the nozzlesthemselves scales linearly with P. A loss factor of C=5.4×10⁻¹¹mol/(Pa*s) for nozzles of the geometry proscribed in sec I.B.2 wasestimated using a Direct Simulation Monte Carlo Code. FIG. 11 shows amodel used in a circuit analysis of a nozzle array. Fluidic resistanceswere estimated and even distribution of vapor to all nozzles in thearray was verified.

$\begin{matrix}{Q_{c{(n)}} = {Q_{c{({n - 1})}} - Q_{n{(n)}}}} & {{eq}\mspace{14mu}{{II}.B}{.2}} \\{Q_{c{(n)}} = {\frac{P_{n - 1}^{2} - P_{n}^{2}}{L}\frac{h^{3}w}{24\mu\;{RT}}}} & {{eq}\mspace{14mu}{{II}.B}{.3}} \\{Q_{n{(n)}} = {{Cf}\left( {P_{n},P_{T}} \right)}} & {{eq}\mspace{14mu}{{II}.B}{.4}}\end{matrix}$

After 32 segments, a pressure change of less than 0.2% is expected.Pressure driving flow through the nozzles is expected to be constantalong the array.

Rate of vapor generation can be approximated by eq II.B.5, where P isthe pressure of the vapor generation cell, P* is the equilibrium vaporpressure of the organic material in the cell, q is the flow rate ofcarrier gas, and quantity of organic material leaving the cell. γ is aefficiency parameter indicating the degree of saturation of the vaporeffluent from the generator. This is close to unity for a well designedsystem. The vapor pressure of OLED materials can be estimated fromprevious OVJP work. A previous system used 5 sccm of carrier gas at 8Torr to sweep saturated CBP vapor out of source cells towards thenozzle. The instrument was capable of a 2000 Å/s deposition rate, whichsuggests a vapor generation rate of roughly 2×10¹⁴ molecule/s and a CBPvapor pressure of 800 μTorr.

$\begin{matrix}{j = {\gamma\frac{P^{*}}{P}q}} & {{{eq}.\mspace{14mu}{II}.B}{.5}}\end{matrix}$

Assuming a 4 sccm flow of carrier gas through the CBP vapor generator atan operating pressure of 40 Torr, roughly 3.3×10¹³ molecule/s will beproduced. This translates to a deposition rate of 900 Å/s under thenozzle apertures. This, in turn predicts a write speed of 0.6 mm/s.Carrier gas flow rates have been significantly reduced from theseestimated conditions, with flows of 1 sccm and pressures below 10 Torrbeing typical. Despite this change, comparable write speeds ofapproximately 1 mm/s have been observed.

Modeling of organic boats in the vapor generator assume organic isstored in a vented capsule, and is convected away by carrier gas movingover the vent. In this situation, the organic vapor and carrier gasmixture leaves the vapor generator in a 95% saturated condition. It isexpected that separate dilution flows of carrier gas are not necessaryto advance organic material downstream. Furthermore, organic vapor isalready very dilute in terms of mole fraction (˜0.004%). Furtherdilution may merely increase pressure drop and not improve performance.

If flow through the organic vapor source cells is allowed to stagnate,organic material can backstream by migrating upstream to cooler regionsof the tube enclosing the source cell. Assuming the organic vapor sourcecell is maintained at 4 sccm, 40 Torr, and 300° C., a 5 cm heated zoneis sufficient to prevent backstreaming of organic material according tomodeling in COMSOL. Operating conditions may vary significantly fromthese initial predicted conditions, however no serious backstreaming oforganic material has been observed.

A thermal analysis may also be performed to model temperature throughoutan organic vapor jet deposition system.

The temperature of the print head may be modeled. Uniform heating can beachieved by applying an Ohmic heating current directly through the printhead using large area contacts. If necessary, the conductivity of theprint head can be supplemented by an additional thin layer of Ti or Niapplied to its underside. Si s a good conductor of heat, and theborosilicate layer helps to reduce heat transfer to the metal backplane.Experience has shown that, for the geometries actually fabricated, theprint head requires approximately 40 to 60 W of heating to reachoperating an operating temperature of 300° C. when in close proximity toa chilled substrate. Direct measurement of print head temperatures atmultiple points has not yet been feasible, but lower power measurementsin air suggest that temperature is uniform across the print head.Heating current for the print head is driven by an isolated DC powersupply with continuously variable output. This has proven desirable toeliminate both the time domain thermal stress caused by on/off control,and the risk of arcing from a non-isolated power supply.

To good approximation, modeling with Comsol indicates that temperatureis also expected to uniform along cross sections in the region subtendedby the channel.

The temperature of the substrate may also be modeled. Previousunpublished studies in the inventor's laboratories of OLED growth on atemperature controlled substrate chuck has shown that films can be grownat temperatures of approximately 360K without serious loss ofperformance in the resulting devices. This can be taken as anapproximate maximum desirable temperature specification for thesubstrate surface. The heat transfer profile on a substrate in thevicinity of a 20 mm wide nozzle is shown in FIG. 12, based on modeling.The nozzle used for the calculation was a double tapered nozzle with 20μm wide aperture and 5 μm tip to substrate gap. Distances are fromnozzle centerline. The model results are in good agreement withanalytical estimates.

As can be seen in FIG. 12, the nozzles themselves produce hot sportswith 40 W/cm² of heat flux. This compares with an average heat flux of15 W/cm². Since these hot spots are relatively small, there is only amodest increase in temperature compared to the surrounding substrate,which acts as a heat sink. Modeling in COMSOL predicts a steady statetemperature increase of only about 20K in a hot spot. While suchindividual hot spots are easy to manage, the overall heat load from manysuch hot spots is high. Liquid nitrogen cooling may be preferred todrive sufficient heat transfer through a glass substrate to keep thesurface of the substrate below 360K. To this end, the OVJP system hasbeen equipped with a LN₂ feed system that is capable of chilling thesubstrate holder to 150K and below. Depositing organic material at thelow substrate temperatures achieved with this arrangement has thefurther advantage of reducing material migration and improving thesharpness of features.

Heat transfer in vapor generators may also be modeled. The heat transfermodeling of the vapor generators has both a solid and fluid component.Carrier gas is preferably rapidly heated to the organic sublimationtemperature before it comes into contact with the organic source boat atthe base of the generator. Modeling with Comsol indicates that that thishappens extremely quickly, due to the combination of shortcharacteristic length and the relatively high thermal conductivity ofgases at reduced pressure. Assuming a sharp transition in walltemperature between the ambient and heated regions of the source cell, atransition length of only 4 mm is required to heat the gas.

The solid component of the heat transfer problem involves quantifyinghow sharp this transition is. The source cell tube can be modeled as aone dimensional problem. Since the tube is thin walled, radialtemperature gradients are minimal. The contents of the tube are furtherassumed to have minimal thermal mass, an assumption supported by theshort thermal transition length of the carrier gas. The heat equationfor these assumptions and accounting for blackbody radiation is given byeq. II.C.1

$\begin{matrix}{{k\;\tau\frac{\mathbb{d}^{2}T}{\mathbb{d}x^{2}}} = {{\sigma\left( {T^{4} - T_{c}^{4}} \right)} + {h\left( {T - T_{c}} \right)}}} & {{{eq}.\mspace{14mu}{II}.C}{.1}}\end{matrix}$where k is the thermal conductivity of the metal tube, τ is the tubethickness, and T_(c) is the chamber temperature.

Assuming a chamber background pressure of 30 mTorr, the source cell willhave a heat transfer coefficient with the residual chamber gas of h=5.4W/m²K. After linearizing the blackbody radiation term, eq. II.C.1 can betransformed into equation, eq. II.C.2. The characteristic length of thisequation is 2 cm, and gives a rough estimate of the length oftemperature gradient in the vapor generator tube between the heated andunheated regions. Therefore, a minimal length of heated tubing isrequired to warm the gas before it flows past an organic vapor source.

$\begin{matrix}{\frac{\mathbb{d}^{2}T}{\mathbb{d}x^{2}} = {\left( {48\frac{1}{m}} \right)^{2}\left( {T - T_{c}} \right)}} & {{{eq}.\mspace{14mu}{II}.C}{.2}}\end{matrix}$

Mechanical Deformation of a print head can also be modeled. Two possiblecauses of print head deformation have been identified. Thermally inducedstress from uneven heating and differences in thermal expansion maycause the print head to warp. A relatively large pressure differentialmay exist across the portion of the nozzle plate forming the base of thechannel. Properly estimating the lengths of these deformations anddesigning to minimize them is desirable to obtaining a print head thatremains flat during printing, which is in turn desirable for accurateprinting.

It is believed that, by far, the most significant deformations arecreated by thermal stresses in the print head wafer stack. Verticaldeflection due to thermal stress was modeled using the MEMSthermal-structural interaction package in COMSOL. The wafer stack wasmodeled in cylindrical coordinates. Assuming perfect flatness at roomtemperature, once the thin film heater is activated, the wafer stack iscalculated to bow downwards so that the center of the plate is 20 μmlower than the outer rim. Measurements of a print head prototype on aFlexus thin film stress measuring apparatus reveal warping such that thecenter of the wafer is 10 μm higher than the outer rim.

FIG. 13 shows a plot 1310 of the height of the center of a waferrelative to outer rim as function of temperature, as well as a schematic1320 of the setup used to obtain the data. Data for a single wafer isshown as squares, and data for a print head stack is shown as diamonds.Schematic 1320 shows a borosilicate layer 1324 is and a Si layer 1322.Although a displacement on the order of 10 μm is significant withrespect to nozzle spacing, the flatness over the nozzle array itself isexpected to be about 2 μm. The lower number is because the nozzles arerelatively close together near the center of the substrate, and move asa group when the wafer deforms. Since the nozzle array will curvedownward, the plate will not obstruct nozzle positioning, and thenozzles can be brought arbitrarily close. The nozzles themselves may beplaced dead center to minimize substrate curvature. A non contact heightsensor can measure the relative distance between the nozzle tips andsubstrate at operating temperature once properly calibrated. Thermalwarping is expected to be the largest source of error, but a source oferror that can be held at manageable levels.

For the system shown in FIG. 3, the vapor generators themselves areexpected to lengthen by up to 200 μm in response to heating. To preventthis from distorting the print head, the vapor generators may beconnected to the flange by bellows as illustrated in FIG. 3. Thisprevents the flange from pushing against the print head.

The effect of pressure differentials on wafer deformation was alsoconsidered. The maximum bending of a membrane in short axis crosssection in response to an evenly distributed load is given by eq.II.D.2,which is based on Moore, J. H., Davis, C. C., and M. A. Coplan BuildingScientific Apparatus Westview Press; 3rd edition (2002). This is also aresult of the biharmonic stress equation. As before, w is the verticaldisplacement, P is pressure load, and E is the Young's modulus, and t isplate thickness. L is the width of the plate. A 50 μm thick Si membrane1 mm wide is expected to bow out by 40 nm in response to a worst casecross membrane pressure differential of 10,000 Pa. This is also not asignificant deformation, however the inverse cube dependence ofdeformation on membrane thickness means that the membrane becomes muchmore deformable for a thinner rigid nozzle plate. But it is expectedthat these deformations will also be manageable.

$\begin{matrix}{w = \frac{{PL}^{4}}{32{Et}^{3}}} & {{{eq}.\mspace{14mu}{II}.D}{.2}}\end{matrix}$

As mentioned above, one way to address print head deformation is tomeasure the position of the nozzles, since deformation across arelatively small nozzle array may be small, even where there is largerdeformation across the rest of the print head. To this end, a PhiltechRZ-25 demonstrator model was obtained and tested against an ITO glasstarget. The sensor consists of a bundle of optical fibers. Some fibersemit light and others receive light. The degree of coupling betweenemitting receiving fibers is determined by the distance between thebundle and a reflective target. The RZ series sensors feature twoseparate bundles that operate in parallel to correct for differences intarget reflectivity.

The signal was stable to 1 mV, and given a linear response of 0.008V/μm,a precision of 250 nm is can be obtained. The advertised precision is200 nm. The linear range of the sensor is apparently limited by thetransparency of the ITO, and the strength of the reflection from the farsurface. The sensor does not work properly if the ITO target sits on areflective surface. The linear range extends for roughly 300 μm if theITO target is mounted on a matte black surface. This is approximatelyhalf of the advertised value. The full linear range can be obtained whenmeasuring from an opaque target. Other measurement techniques may beused to compensate for these issues. Although the range of the sensor islimited, 300 μm is more than adequate for fine control of stageelevation. A non-reflective substrate holder is preferred. FIG. 14 showsa plot of displacement vs. voltage for calibration of a PhilTech RZ-25displacement sensor on an ITO target.

FIG. 15 shows a process flow for preparing silicon and borosilicatewafers for microfabrication. Silicon on insulator (SOI) wafers 1510 maybe obtained from Ultrasil Inc (Hayward, Calif.). The SOI wafer 1510 maybe used to make the nozzle plate. As received, the wafers are 100 mmdiameter, with a 100 μm thick Si device layer 1516 separated from a 315μm thick Si handle layer 1512 by a 1-3 μm SiO₂ oxide layer 1514. Doubleside polished (DSP) 100 mm diameter, 500 μm thick borosilicate glasswafers 1550 are obtained from University Wafer (Cambridge, Mass.).

Masks for all four photolithographically defined patterns are producedusing the LNF mask maker and the SOP for developing chrome masks. Priorto the start of photolithographic processing, an LPCVD Si₃N₄ hard masklayer 1522 is grown over the SOI wafers on both sides, as illustrated bywafer 1520. Similarly, a hard mask layer 1562 of 20 nm Cr/500 Au/20 nmCr/500 nm Au is deposited on each side of the borosilicate glass wafersin preparation for etching, as illustrated by wafer 1560.

FIG. 16 shows steps of Si and borosilicate processing used to fabricatea print head.

The Si processing was as follows. The Si₃N₄ layer from FIG. 15overlaying the SOI wafer is patterned with the nozzle inlet mask usingSPR 220 photoresist. The Si₃N₄ layer over the nozzle inlets is thenetched away with a 150 s deep reactive ion etch. The wafer is thenetched in a 85° C., 50% by weight KOH solution for 100 min to form theinner tapered surfaces of the nozzles. The result of this step is shownin wafer 1630. Windows in the nozzle plate for displacement sensing andoptical alignment are also cut at this time (not shown). The insulatorlayer of the SOI wafer forms an etch stop which defines the outlet ofeach nozzle. The Si₃N₄ layer is then removed with either a reactive ionetch or hot phosphoric acid etch. The result of this step is shown inwafer 1640.

The borosilicate processing was as follows, and was adapted from CiprianIlieseu, F. E. H. Tay and J. Miao Sens. Act. A. 2 (133), 395-400 (2007).The metalized borosilicate glass wafers from FIG. 15 are coated on bothsides with 10 μm AZ-9260 resist and photolithographically patterned withthe channel pattern on one side and the via pattern on the other. Themetal hard mask is then etched away with alternating dips on TranseneGE-8148 gold etchant for 4 min and Cyantek CR-14 chromium etchant for 30s. The result of these steps is shown in wafer 1610. The vias side ofthe wafer is affixed to a backing wafer with paraffin wax to protect itfrom etchant. The channel side is exposed. The wafer is immersed in 49%HF solution until the channels are etched to 100 μm. Etch depth isverified using a stylus profilometer. The desired amount of etching wasachieved in approximately 15 min. The wafer is removed from its back andcleaned with hot trichloroethylene. The channel side is then affixed tothe backing wafer with wax and the vias are etched using the HFsolution. This etch goes through the wafer. The desired amount ofetching was achieved in approximately an hour. The wafer is then cleanedwith hot trichloroethylene and the metal mask is removed with gold andchromium etchants. The result of these steps is shown in wafer 1620. Itshould be appreciated that the illustrated cross section shows a channelhaving vias at each end, and that there are other regions of the waferwhere there are no channels, vias, or both.

Anodic bonding is used to join the dissimilar layers of the print head.The order of bonding described is preferred for this particularembodiment due to the electrochemical nature of the anodic bondingprocess. Anodic bonding may be used to join a sodium containing glass toa metal or semiconductor. Once heated to 300-400° C., Na⁺ in the glassbecomes mobile. A potential of about 1000 V is applied from an anodeunder the metal layer to a cathode above the glass. Mobile carriers inthe glass move away from the interface leaving an oppositely chargeddepletion region. The motion of cations leaves dangling oxygen atoms inthe glass free to oxidize the metal interface, forming a chemical bondbetween the two materials. Anodic bonding is described in G. Wallis,Field Assisted Glass Sealing, 2(1), Electrocomponent Science and Tech,1975 K. M. Knowles et al., Anodic bonding, 51(5), InternationalMaterials Rev., 2006.

The wafer bonding steps were as follows. The Borosilicate and Si wafersare prepared for bonding with a piranha clean. Afterward, the Si waferis dipped in dilute HF to remove surface oxide. The wafers are thenvisually aligned and then placed in a Suss SB-6 Bonder. They are bondedin vacuum at a temperature of 400° C. by applying a voltage of 1000V for20 min. The result of this step is shown in wafer stack 1650. Thepositive potential is applied to the Si side. In one embodiment, theback side of the borosilicate layer may be bonded to a Kovar backplaneusing anodic bonding. This may provide the print head with a more robustsealing surface.

Once bonded, the handle layer of the Si wafer is to be removed. Thewafers are mounted to an aluminum chuck with paraffin wax. They are thensubmerged in a trilogy etch of 90% HNO₃, 9.5% HF, and 0.5% CH₃COOH stocksolutions. The wafer is continuously rotated and the etch bath isaerated with N₂ to ensure an even etch. The desired amount of etchingwas achieved in approximately 50 min, and etching is allowed to proceeduntil the SiO₂ etch stop is visible. The etch is preferably stoppedpromptly, due to the poor selectivity of trilogy etchant for Si overSiO₂. The wafers are removed from the chuck and remaining wax isdissolved with hot trichloroethylene. Since trilogy etchant does notstrongly select for Si over SiO₂, a more selective finishing step ispreferred. Remaining Si over the SiO₂ etch stop is removed with deepreactive ion etching (DRIE). DRIE is not used to remove all of the Sibecause it is significantly slower than trilogy etchant.

After handle layer removal, the SiO₂ covered underside of the wafer iscoated with AZ-9260 photoresist and patterned so that regions that willbe raised at the end of the process are covered with resist. ExposedSiO₂ is removed with a reactive ion etch (RIE). The result of this stepis shown in wafer stack 1660. The non-raised portions are then etched 40to 50 μm by DRIE. Completion of this etch is monitored by profilometery.The result of this step is shown in wafer stack 1670.

Afterward, photoresist is stripped and the remaining SiO₂ hard mask isremoved with RIE.). The result of this step is shown in wafer stack1680. Ohmic contacts consisting of 800 nm Al, 50 μm Pt, and 500 nm Auare evaporated onto opposite sides of the wafer to allow the wafer to beaddressed by a heating current. An additional thin blanket coating of Tican be added over the nozzle plate if the native Si is not sufficientlyconductive for good heating. Finally, Cu foil leads are affixed to theelectrodes with high temperature conductive epoxy.

The general structure of the OVJP print head and vapor generators asfabricated is as follows. Organic sources are stored at the end of glassstalks which are inserted into tubes that extend into a vacuum chamberand are heated at their far end. This system eliminates the problem ofhaving to disconnect a high temperature seal, or undo a complexassembly, to refill material. OVJP operates at much higher pressures andmuch lower flow rates than OVPD, which may lead to a higher vaporresidence time. The volume between the organic vapor sources and thenozzle array is kept as short as possible to eliminate unnecessaryvolume. Modeling indicates that separate source and dilution flows arenot helpful at this length scale. As a result, there is no explicitprovision for them, although these features could be readily added.

In one embodiment, the form factor of the OVJP system allows it to beattached to an 8″ ConFlat port.

Heat boots are fabricated by first coating stainless steel tubes with athin coat of Cotronics Resbond 919 high temperature ceramic adhesive.The coated region is 2 in wide and starts 0.125 from the tip of thetube. This coating provides a resistive surface on which to wrapNichrome wire. A 0.005″ diameter wire wrapped for 50 turns will give theheater a resistance of 220Ω. Once wrapped, the heater is sealed withanother coat of Resbond 919 and cured overnight. The tubes can be platedwith Ag if desired to reduce emissivity. These homemade heaters arecompact and powerful, and do not produce particulates like fiberglassinsulated heat tapes. Unlike commercial heat tapes, ceramic does notoutgas once cured.

FIG. 17 shows an exploded drawing of an OVJP feedthrough. Two organicvapor sources are illustrated for ease of illustration, but largernumbers of sources may be used, such as the six shown in FIG. 3, or evenmore Manifold 1710 acts as a feedthrough, through which gas passes onits way to the print head, and through which organic source boats thatare located very close to the print head during deposition may be easilyand conveniently removed and replaced without breaking thermal seals.Tubes 1720 that lead to the print head, as illustrated in FIG. 3, extendfrom manifold 1710. Gas feeds 1730 may be attached to tubes 1720. Gasfeeds 1730 may include ports for gas, as well as ports to allow for thepassage of source boats. Ultra torr fittings 1740 are attached to gasfeeds 1730, and provide an easily breakable and replaced hermetic sealthrough which source boats may be passed. Organic source boats 1750 aredisposed on stalks 1760. Stalks 1760 may be inserted through ultra torrfittings 1740, gas feeds 1730, tubes 1720 and manifold 1710, andextended further through, for example, bellows 340 of FIG. 3 and relatedtubes until source boats 1750 are in close proximity to a print head.Ultra torr fittings 1740 provide a seal.

Specific non-limiting materials and dimensions that were used tofabricate an OVJP system are as follows. 0.375″ steel tubes 1720 frommanifold 1710 are terminated with swagelok T tube fittings (gas feeds1730). Swagelok Ultratorr fittings 1740 are clamped into the farjunction of the T fitting. A long glass stalk 1760 which contains anorganic boat 1750 at its tip is inserted through the UltraTorr fitting1740. Stalk 1760 extends all the way to the print head. Carrier gas isfed into the vapor generators from the middle connection of the T tubefittings.

It is preferred that a motorized x-y motion stage is provided to movethe substrate relative to the nozzle array in order to draw patternedorganic films using OVJP. The planes of the nozzle array and thesubstrate are preferably held as close to parallel as possible for thesystem to work well. For best results, substrate holder preferably has aflatness of >±1 μm per cm of linear travel. The bearings on which thesubstrate holder moves are preferably placed underneath the holder. Thesimplest arrangement would be to put two complete, stacked linearactuators inside the chamber. These actuators can sit on top of a dualtilt stage for fine leveling adjustment. This control can be manual,since alignment can be done prior to chamber evacuation. The zadjustment, however, is preferably motorized to provide height control.Because space within the chamber is at a premium, a z actuator ispreferably incorporated with a vacuum linear positioner and mountedoutside of the chamber. A manual rotation adjustment may similarly bemounted outside the chamber.

The OVJP system is preferably equipped with motorized x-y motion stages.Motion parallel to line orientation may be provided by a vacuum preparedAerotech ATS-50 stage. Motion perpendicular to line orientation is maybe provided by a Newport optical stage modified with a custom actuator.

The substrate holder may be made from aluminum with an anodized finishon top for compatibility with the non-contact height sensor. It sits ontop of a copper cooling block which is fed liquid nitrogen coolantthrough flexible tubes. The holder can be removed through an adjacentglovebox to allow samples to be loaded and unloaded in an non-oxidizingenvironment. Thermal contact of substrate, holder, and cooling block maybe enhanced with thin coatings of SPI Apezon cryo grease.

A PhilTech RZ-25 optical displacement sensor may look through a windowin the print head to measure distance to the substrate. The sensorconsists of a fiber optic bundle with emitter and receiver fibers. Thecoupling between the two fiber types is dependent on the distancebetween the bundle tip and a reflecting surface. The sensor tip is heldby a fiber optic holder, which is in turn attached to one of the polesconnecting the print head to the flange. The sensor signal istransmitted by an optical fiber bundle to a sensor outside of thechamber through a vacuum feedthrough.

Alignment with landmarks on the substrates is a preferred way to achievepositioning to overwrite features on the substrate. The print headpreferably has separate windows to allow optical alignment. The chambercan be fitted with CCD cameras, appropriate lenses, lighting andsoftware to allow alignment. These features are not present in currentdesigns, but are well known and may be readily incorporated an OVJPsystem.

FIG. 18 shows a configuration of an OVJP system with alignment opticsand height sensor installed. The OVJP system has many of the samefeatures that are illustrated in FIG. 17. In addition, the OVJP systemof FIG. 18 includes a camera system useful for optical alignment. Thecamera system includes a camera 1810, projection lens 1812 and objective1814. Appropriate openings may be readily provided in the manifold andprint head. The OVJP system of FIG. 18 also includes a height sensor1820. The configuration of FIG. 18 was not actually reduced to practice,but could be readily practiced based on the disclosure herein.

The OVJP system may be operated as follows.

The nozzle may be squared to the substrate plane, and the height sensorcalibrated. The planes of the print head and substrate are madecoincident with the print head at room temperature and the chambervented. Front to back alignment is performed using a laser level and amirror at the back of the substrate stage. Left to right alignment canbe implemented using a feeler gauge to equalize the print head tosubstrate gap on each side of the substrate.

Organic material is spooned into a source boat at the tip of aborosilicate glass stalk. A thermocouple is threaded through the innerdiameter of the stalk, to the stricture separating the stalk and boatand tightened in place. The stalk is inserted through the Ultratorrfitting at the top of the deposition chamber. The stalk is advanceduntil its tip is within 3 mm of the print head. The stop position ispreferably measured in advance to prevent damage to the print head.

A substrate is placed in the vented chamber. Gas feed lines are openedto a bypass “Eustachian” tube which equalizes pressure between the printhead vias and the chamber. The chamber is evacuated, and the OVJP isslowly heated to operating temperature. Once the OVJP is at high vacuum,a flow of LN₂ is established to the substrate stage. Finally the gasfeed lines are sealed from the Eustachian tube.

After leveling the stage is lowered to give the nozzles room to movedownward as the print head heats. The print head and vapor generatorsare then brought to operating temperature. Hard contact between theprint head and substrate can be inferred based on either a suddenincrease in the thermal load of the print head or by a sudden increasein organic source cell pressure when the print head is in use. Thereading of the height sensor can now be zeroed.

Approximately 1 sccm of carrier gas is fed into each depositing source.Organic vapor sources should be heated to 200° C. to 300° C. dependingon the material inside. The print head is heated to 300° C. The nozzletips are brought to 10 μm of the substrate. A fine z adjustment may belocked into a feedback loop with the height sensor (not yetincorporated). The system is now depositing, and the patterns aregoverned by the motion of the x and y stage motors. Once the pattern isprinted, deposition can be terminating carrier gas flow and reopeninggas feed lines to the Eustachian tube.

Following deposition, the substrate is lowered away from the print head.The print head and organic source cells are both slowly cooled. All ofthese are preferably below 100° C. before the chamber is vented. Thechilled stage is warmed above 0° C. as well.

Preferred operating conditions include a chamber pressure of less than 1mTorr and a substrate holder chilled to −100° C. Organic vapor is forcedinto the print head by a pressure of 1 to 50 Torr of inert gas at a flowrate of 1 standard cubic centimeter per minute per source via. Vapor canbe mixed or diluted by combination of flow with other sources. The printhead is maintained approximately 10 microns from the substrate surface.The substrate moves beneath the print head at a rate of 0.5 to 2 mm/s.Optical micrographs of lines of 35 nm thick Aluminumtris-(quinoline-8-olate) are shown in FIG. 19. Under preferred operatingconditions, the print head can draw continuous lines organic materialapproximately 20 μm wide. FIG. 19 shows optical micrographs of 35 nmthick lines of AlQ, Aluminum tris(quinoline-8-olate), drawn using theOVJP print head, at two different magnifications (images 1910 and 1920).These lines are surrounded on each side by zones of extraneousdeposition which are estimated to be no more than 10 μm wide. This issupported by scanning electron microscope (SEM) and atomic forcemicroscope (AFM) images. FIG. 20 shows SEM images of the 35 nm thicklines of AlQ drawn using OVJP print head at two different magnifications(images 2010 and 2020). FIG. 21 shows atomic force micrograph of the 35nm thick AlQ lines drawn with OVJP, including a two dimensional viewwhere height is shown by grey scale (image 2110), and a trace ofthickness in perpendicular to major axis of line using AFM (image 2120).Both width and thickness of the lines can be estimated from the crosssectional AFM trace.

To provide high resolution patterning of multicolor OLED arrays, OVJP ispreferably capable of depositing material in tightly defined lines withminimal bleeding between lines. Indirect measurements of overspray oforganic material in the regions between lines have been performed.

In one test, very thick lines were grown by moving the stage slowlybeneath the print head. While these features are much thicker than thoseused in practical electronic devices, growing these lines allowed subtlefeatures such as overspray tails to be magnified sufficiently to bemeasurable. The thickness cross section of these lines was thenevaluated by profilometry. Lines were deposited having a thickness of upto 20000 angstroms (2 nm) in the region where deposition is desired.Beyond the measured 20 μm line width, overspray tails of 100 nm or lessare measured that appear to extend for 10 μm beyond the line edge. Thesefeatures are approximately 100 times thicker than would be found inOLEDs. Assuming that overspray thickness is proportional to featurethickness, this would imply that 1 nm or less of overspray can beexpected in the proximity of drawn lines. FIG. 22 shows images of theselines, including an optical micrograph 2210 and a profilometer trace2220.

Spatially resolved photoluminescence was used to probe overspray in theregions between thin film lines. Thickness calibrated measurements weretaken on a specially constructed linescanning microscope. This systemhas a resolution of approximately 5 μm and a detection threshold ofapproximately 2 nm of AlQ tracer material. An initial scan revealed abackground overspray of approximately 5 nm. Interestingly, the height ofoverspray does not appear to be correlated to distance from a line orthe height of the nearest line. This suggests that the overspray waslaid down at startup rather than during the actual printing and can beminimized by improving the startup procedure. The thickness of linesdecreases significantly for nozzles further downstream of the organicmaterial source. This is believed to be due to fabricating a particularprint head with shallower fluidic channels to improve crack resistance,and the effect can readily be removed by using larger channels. Linescandata is shown in FIG. 23. FIG. 23 shows thickness corrected linescandata from OVJP drawn sample of AlQ.

A Zeiss confocal epifluorescence microscope at the Microscopy and ImageAnalysis Laboratory at the University of Michigan was used to probeoverspray at higher spatial resolution. This microscope has a similardetection threshold to the linescanner but is otherwise much morecapable. FIG. 24 shows a region of OVJP deposited lines analyzed usingthis system. Little or no signal was detected between the lines,suggesting an overspray thickness of 3 nm or less. While outputs fromthis tool are preferably calibrated with samples of known filmthickness, the absence of signal from regions between lines suggeststhat little, if any, material is settling in these regions. FIG. 24shows a confocal epifluorescence micrograph of OVJP drawn lines of AlQ.Image 2410 is a two dimensional image with fluorescent intensity shownby grayscale. The vertical arrow shows the direction of the intensityprofile scan illustrated in image 2420, which shows the intensity offluorescence along the line as function of distance.

It is understood that the various embodiments described herein are byway of example only, and are not intended to limit the scope of theinvention. For example, many of the materials and structures describedherein may be substituted with other materials and structures withoutdeviating from the spirit of the invention. Inventive nozzle geometriesdescribed herein may be used in a wide variety of OVJP systemconfigurations and print heads in addition to the specific embodimentsillustrated herein. Similarly, inventive print head concepts describedherein may be used in a wide variety of OVJP system configurations inaddition to the specific embodiments illustrated herein. The presentinvention as claimed may therefore includes variations from theparticular examples and preferred embodiments described herein, as willbe apparent to one of skill in the art. It is understood that varioustheories as to why the invention works, and modeling of specificconfigurations, are not intended to be limiting.

The invention claimed is:
 1. A device, comprising: a print head; and afirst gas source hermetically sealed to the print head, the print headfurther comprising: a first layer further comprising a plurality ofapertures, each aperture having a smallest dimension of 0.5 to 500microns; and a second layer bonded to the first layer, the second layerfurther comprising a first via in fluid communication with the first gassource and at least one of the apertures, wherein the second layer ismade of an insulating material, a third layer disposed between the firstand second layers and bonded to the first layer and the second layer,wherein the third layer further comprises a channel that provides fluidcommunication between the first via of the second layer and apertures ofthe first layer; and wherein at least one of the first layer and thesecond layer is configured to be heated.
 2. The device of claim 1,wherein the first layer further comprises a channel that provides fluidcommunication within the first layer between the first via of the secondlayer and apertures of the first layer.
 3. The device of claim 1,wherein the third layer further comprises a heat source.
 4. The deviceof claim 1, wherein a plurality of apertures are in fluid communicationwith the first gas source.
 5. The device of claim 1, wherein the printhead further comprises a microelectromechanical switch adapted to blockor allow fluid communication between the first via and the at least oneof the apertures depending upon the state of the switch.
 6. The firstdevice of claim 1, wherein at least one aperture is formed in aprotrusion from the print head.
 7. The first device of claim 1, whereinthe thickness of the print head is between 50 and 500 microns.
 8. Thefirst device of claim 1, wherein the second layer further comprises achannel that provides fluid communication within the second layerbetween the first via of the second layer and apertures of the firstlayer.